Thermometric rheostat.



No. 800,792. PATENT-ED OUT. 3, 1905.. W. H. BRISTOL. THERMOMBTRIC RHEOSTAT.

APPLIOATION FILED APE. 18.1905.

UNITED STATES WILLIAM H. BRISTOL, OF NEIV YORK, N. Y.

THERIVIOIVIETRIC FlHEOSTl-Tlln Specification of Letters Patent.

Patented Oct. 3, 1905.

Application filed April 18, 1905. Serial No. 256,211

T0 at whom, it pea/y concern:

Be it known that I, WILLIAM H. BRISTOL, a citizen of the United States of America, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Thermometric Rheostats, of which the following is a specification.

My invention relates to thermometric rheostats in which resistance is cut in or out by the fluctuation in the height of a column of liquid, due to variations in temperature; and it has for its object to render such devices more readily constructed, less liable to injury, and to allow for a minimum total resistance when required.

For this purpose my invention consists, essentially, of a liquid thermometric device in the shank of which is a resistance wire, rod, or filament provided with leads of larger cross-section than said resistance-wire.

My invention will best be understood when described in connection with the accompanying drawings, in which- Figure 1 illustrates a preferred form of the device. Fig. 2 illustrates a modification.

Similar numerals of reference designate corresponding parts throughout both views.

Referring now to the drawings, 1 is a thermometer containing a liquid 2, preferably mercury, offering a cross-section of high conductivity as compared with that of a resistance wire, rod, or filament 3, inserted usually in the bore of the thermometer-shank 4c. This wire, rod, or filament 3 is connected to the leads 5, of considerably larger cross-section, which pass out of the shank 4; and are then connected as desired. It will readily be understood that as the mercury rises and falls with variations in temperature a corresponding portion of the wire, rod, or filament 3 will be short-circuited, or vice versa, thus cutting out or in resistance in accordance with the length of the wire, rod, or filament immersed.

Although I have shown the wire 3 looped, I do not wish to restrict myself to any particular form, as the wire may pass entirely through the thermometer or be broken.

In Fig. 2 I have shown a form by which a large amount of resistance may be thrown in or out with a comparatively small change in the height of the mercury column. In this construction the body of the thermometer is provided with a bulb of considerable length and Width, and the shank is formed to correspond, thus permitting of the insertion of the coil 3 into the shank. This coil may consist of a larger number of windings or convolutions about a non-conducting core 6, so wound as to be insulated from one another.

I am aware that thermometric rheostats of a somewhat similar nature are known, such as the compensating device shown in my prior patents, No. 776,491, of December 6, 190A, and No. 783,503, of February 28, 1905. I am also aware that considerable difliculty is experienced with the fine resistance-wire leading from these rheostats, in that it frequently breaks or is burned out in attempting to fuse it into the glass. As a comparatively large resistance is required and as this wire must be placed within a comparatively short length, the wire is of necessity very thin and likely to break after leaving the device or burn out in fusing it into the glass. In fact, it is necessary sometimes to make it so thin as to render the manufacture and use of such devices almost impracticable. It is the purpose of my invention to obviate this difiiculty and to render the manufacture and use of such thermometric rheostats perfectly practicable; also, to reduce the size of the rheostat and to allow for a lower total resistance when this is desirable. For this purpose I do not expose the thin resistance-wire beyond the shank of the thermometer, where it may be easily broken, but carry the two leads 5 of considerably larger cross-section into the shank of the thermometer. These leads are of such cross-section that they may be readily fused into the glass without fear of burning them and will form substantial conductors, which may be connected and handled without fear of breaking. In practice I prefer to use a wire, usually platinum, of which a portion 3, forming the resistance part, has been considerably reduced in cross-section by swaging or otherwise reducing the portion of larger cross-section forming the leads 5. I am thus enabled to obtain a perfectly continuous wire, the reduced section of which, as well as a small portion of the leads, is placed a suliicient distance within the shank of the thermometer to enable the leads to be fused into the glass. I have also found an electric weld between the line resistance-wire and the leads to make a very good form of connection. By constructing a thermometric rheostat after this manner I am able to concentrate the resistancethat is, by using an extremely fine resistance wire, which is impossible under the old construction, small fluctuations of the mercury column will effect a comparatively large change in resistance. The size of the mercury-bulb, as well as the entire rheostat, may therefore be made very small. I have also found it desirable, especially in thermoelectric measurements, to maintain the total resistance of the circuit as low as possible. When using this rheostat, therefore, as a compensator, as described in my previous patents, No. 776,491, of December 6, 1904, and No. 783,503, of February 28, 1905, I have the resistance reduced as low as possible, since the leads 5 of comparatively low resistance are brought very close to the actual working part of the resistance-wire 3, thus avoiding the introduction of any superfluous resistance into the circuit. The resistance of the entire rheostat in some instances approximates 0.2 of an ohm. In the old device this resistance-wire was carried considerably beyond the effective portion, extending even beyond the instrument. This difference in resistance is appreciable when working under conditions where it is desirable to keep the total resistance of the circuit approximately one ohm.

What I claim as my invention, and desire to secure by Letters Patent, is

1. A thermometric rheostat comprising a liquid thermometric device containing a resistance wire or filament connected within said device to leads of larger cross-section than the said resistance wire or filament and adapted to be short-circuited or vice versa by the liquid.

2. A thermometrie rheostat comprising a mercury-thermometer containing within its shank a platinum leading-in wire, the active portion of which is of reduced cross-section forming a resistance adapted to be short-circuited or vice versa by the mercury.

In testimony whereof I have signed my name to this specificatiomin the presence of two subscribing Witnesses,this 17th day of April,1905.

WILLIAM H. BRISTOL.

Witnesses:

Geo. W. EISREDROW, ROENA H. YUDIZKY. 

